Colloidal suspensions of magnetic particles which have been referred to as ferromagnetic fluids or ferrofluids are well known and have been proposed for application in such diverse areas as rotary seals, liquid brushes, liquid bearings, artificial muscles, fluidic valves, contact point lubricators, magnetic inks, cleanup fluids for oil slicks on water, and when suspended in a host fluid for use in applications such as magnetic toys and magnetic displays.
It is known that various conventional colloidal suspensions of magnetic particles such as magnetite (Fe.sub.3 O.sub.4) stabilized by a surface active agent when brought into contact with a host liquid tend to degrade over a relatively short period of time whereby their magnetic properties are lost. In particular, such degradation occurs wherein the colloidal suspension changes into a solution in the host liquid or forms a highly viscous shapeless often nonmagnetic lump which can no longer be broken up into droplets of colloidal size and if broken up can not be recollected into one ferromagnetic fluid poll by a magnetic field. It is believed that the degradation occurs through leaching out of the surface active agent from the aqueous phase into the host fluid and/or by hydration of Fe.sub.3 O.sub.4.
For a further discussion of colloidal suspensions of magnetic particles or ferrofluids, the following exemplary literature articles are of interest:
1. "Magnetic Fluid, An Introduction to the Phenomena and Applications of Magnetic Fluid Technology", Manual 273, Ferrofluidics Corporation, April 1973, PA1 2. R. Keiser and Gabor Miskolczy, "Some Applications of Ferrofluid Magnetic Colloids", IEEE on Magnetics Mag. 6, No. 3, September 1970, PA1 3. R. Keiser and G. Miskolczy, "Magnetic Properties of Stable Dispersions of Subdomain Magnetic Particles", J. Appl. Phys. Vol. 41, No. 3, 1064-1072, 1 March 1970. PA1 A. water; PA1 B. a water-immiscible liquid phase comprising a solution of: PA1 C. a colloidal suspension in the discontinuous or continuous phase of the emulsion of ferromagnetic particles and a surfaceactive agent in an amount at least sufficient for stabilizating the ferromagnetic particles in the desired discontinuous or continuous phase of the emulsion; PA1 D. the relative proportions of the nonpolar hydrocarbon and the halogenated aliphatic hydrocarbon being such that the density of the continuous phase and the density of the discontinuous phase are substantially equal to each other; and PA1 E. the nonpolar hydrocarbon and halogenated aliphatic hydrocarbon being mutually soluble in each other and being compatible with the surface-active agent.
Heretofore, various known colloidal suspensions of magnetite stabilized by surface active agents such as sodium oleate in water when contacted with a host organic liquid degraded within a few weeks resulting in the decomposition of the colloidal suspension in water, such as by escape of the magnetite from the aqueous phase to the organic phase, by swelling of the ferrofluid phase, or by hardening of the ferrofluid phase. This, in turn, resulted in loss of the magnetic properties of the aqueous phase and/or of the fluidity of the aqueous magnetic phase. Moreover, even when sufficiently stable, such suspensions suffer from the disadvantage of requiring relatively large magnetic forces to be moved through the host liquid.
Accordingly, it is an object of the present invention to provide a ferromagnetic fluid dispersed in a host solution wherein the dispersion or emulsion has a long shelf life (i.e., is stable for a long period of time against deterioration while sitting undisturbed or while being agitated mechanically or magnetically).
In addition, it is an object of the present invention to provide a ferromagnetic fluid emulsified in a host liquid which forms relatively small droplet size. In addition, the objects of the present invention include providing ferromagnetic fluid droplets which have small inertia, are equidense with the host fluid and require very little force to be moved through the host solution.